clear all; close all; clc;

R = 100;
C = 33e-6;

RC = R*C;

Tmod = 10*RC;
T = RC / 1000;

t = 0:T:Tmod;


E = 0*(t<Tmod/4)+3*(t>=Tmod/4);

U = nan(1, length(t));
dU = nan(1, length(t));

U(1) = E(1); dU(1) = 0;
U2 = U;

for k = 2:length(t)
    
    U(k) = U(k-1) + dU(k-1)*T;
    dU(k) = (E(k) - U(k)) / RC;
    
    
    U2(k) = (RC*U2(k-1) + E(k)*T) / (RC + T);
end

figure;
plot(t, E, t, U, t, U2)
xlabel('t, sec');
ylabel('U, V');
